1. Field of the Invention
The present invention relates to a bootstrap inverter circuit, specifically, to a bootstrap inverter circuit that decreases the voltage of the voltage raising point.
2. Descriptions of the Related Art
In recent years, thin-film transistor liquid crystal displays (TFT-LCD) have been widely utilized in personal computer displays, TVs, cell phones, digital cameras, etc. Generally, to reduce the cost of manufacturing, the single process technique, such as the PMOS or NMOS process, is utilized to simplify the process of manufacturing thin film transistor arrays. These thin film transistor arrays require a steady and higher driving voltage when used in a liquid crystal display. Therefore, a logic level of a general circuit must pass through a peripheral driving circuit so that it can be transformed into a higher voltage for providing a driving voltage for the liquid crystal display.
FIG. 1A illustrates a circuit diagram of a prior bootstrap inverter circuit. The bootstrap inverter circuit is composed of N-type transistors, which comprises an input end Vin, a first capacitor 101, a second capacitor 103, and an output end Vout. A contact point 105 in FIG. 1A is the voltage raising point of the bootstrap inverter circuit. Please refer to FIG. 1B where the symbol 107 represents a voltage waveform of the output end Vout in FIG. 1A and the symbol 109 represents a voltage waveform of the contact point 105. The waveform in FIG. 1B is generated by setting the threshold voltage (Vth) to 4V in all N-type transistors, 20V as the first power source VDD, 0V as the second power source VSS, 0.2 pF as the first capacitor 101 and 1 pF as the second capacitor 103. When the input end Vin inputs a low voltage signal, the voltage signal of the output end Vout will be transformed into the voltage level of the first power source VDD, and the voltage of the contact point 105 will be raised to the voltage level of (2VDD-Vth), i.e. about 36V. Because the voltage level of the voltage rising point is so high, the structure of the transistors has a high likelihood of being damaged. Consequently, the stability and the reliability of the bootstrap inverter circuit would also be affected.
In conclusion, when a single TFT process technique is utilized to manufacture bootstrap inverter circuits, problems of high voltage levels in the voltage rising points may result. Consequently, it is important to find a way to decrease the voltage level of the voltage rising points, so that the stability and reliability of the circuits are not compromised.